1. Field of the Invention
This invention relates to an optical system compensating apparatus for automatically compensating for the shake of a picture when shooting a video camera.
2. Description of the Related Art
Recently, usage of video cameras and like video instruments has, not been limited to broadcast purposes and professionals, but usage is spreading wide among the general public. For home usage, the portability and manageability are regarded as important. The prevailing trend to minimize the size of the camera increases the opportunities for holding the camera by hand when shooting. With a person unaccustomed to the camera, when doing hand-held shooting, camera shakes are apt to occur, so that, as the picture is not stabilized against them, it will jiggle on the monitor. Such a motion introduced by the camera shakes into the entirety of the picture detracts from the quality of the picture itself, giving an unpleasant impression to the viewer.
A shake compensating apparatus is disclosed in U.S. Pat. No. 4,788,596, U.S. patent application Ser. No. 880,152 filed on Jun. 30, 1986, U.S. patent application Ser. No. 319,658 filed on Mar. 6, 1989, and others.
It is also known to provide an apparatus having means for detecting motion of the object image irrespective of the shake detection as, for example, disclosed in U.S. Pat. No. 5,031,049 filed on May 23, 1985, U.S. Pat. No. 4,872,058 filed on Oct. 8, 1987, Ser. No. 237,511 filed on Aug. 26, 1988 and Ser. No. 240,915 filed on Sep. 6, 1988.
Now, concerning the apparatus for stabilizing the image against the shakes of the camera, the feature that constitutes the premise of the invention is first explained. There has been a previous proposal of such a compensating apparatus for optical system as shown in FIG. 1. The apparatus includes a variable angle prism 10 in the form of the so-called binary lens capable of varying the direction of its optical axis and a photographic optical system 12 comprised of various lenses. The photographic optical system 12 forms an image on the imaging plane of an image sensor 14, for example, a CCD, in which the optical information is photoelectrically converted to produce video signals. The video signal output from the image sensor 14 is converted to a formatted form, for example, NTSC, by a processing circuit 16. The apparatus further includes a shake detecting circuit 18 receptive of the output 16a of the processing circuit 16 for producing an output representing the amount of temporal variation of the picture between successive two fields or frames and the direction of that variation, an integration circuit 20 for integrating the output of the shake detecting circuit 18 to obtain the direction of compensation and the amount of compensation for the temporal variation of the picture, and a drive circuit 22 for driving the variable angle prism 10 based on the output of the integration circuit 20.
Of the parts of FIG. 1, the photographic optical system 12, the image sensor 14 and the processing circuit 16 are well known, since these constitute the general form of the video cameras their explanation is omitted. The shake detecting circuit 18 computes the position of a characteristic point of the picture, for example, an edge, or the center of gravity, during transferring of one field or one frame when the amount of shake and the direction of shake between the successive two fields or frames is determined from the video signal 16a output from the processing circuit 16. An example of the construction of the shake detecting circuit 18 is shown in FIG. 2.
Referring to FIG. 2, the video signal 16a output from the processing circuit 16 enters an edge distribution detecting circuit 24 for detecting the distribution of edges of an object in the photographed picture. For example, from the number of edges in the predetermined vertical or horizontal line, the characteristic of the object is detected. The detection information for one picture from the edge distribution detecting circuit 24 is stored in, and, after the delay of one field period, is output from a delay circuit 26. A comparison circuit 28 compares the edge distribution information of the edge distribution detecting circuit 24 with the output (one picture earlier edge distribution information) of the delay circuit 26 to produce an image shake detection signal 18a representing the amount of shake and the direction of shake of the picture. By such an arrangement, the shake detecting circuit 18 produces the shake detection information 18a indicative of a change in the image position between the pictures, that is, the shake of the image, and the motion of the object in each period of one field or one frame.
The integration circuit 20 accumulates the shake detection information 18a of the shake detecting circuit 18 over successive several fields or several frames. The details of the integration circuit 20 are shown in FIG. 3. The output of an adder 30 is rid of the information on a band of frequencies at which compensation is not aimed, in words, the other band of frequencies other than that of a component attributable to the shaking, by passing the output through a band-pass filter 32. The output of the band-pass filter 32 is stored in a memory 34 and, after one field period, is output therefrom to the adder 30. In other words, the memory 34 functions as a one-picture delay element. The adder 30 adds information of the shake between the present and the preceding pictures to the shake detection information 18a output from the shake detecting circuit 18. In more detail, the amount of shake and the direction of shake obtained one picture before are combined in vector with the amount of shake and the direction of shake obtained two pictures before. Since the frequencies of the shaking of the camera generally fall within a range of from 0.5 Hz to 10 Hz, the frequency components other than the necessary band are removed by the band-pass filter 32. The output of the band-pass filter 32 is delayed by the memory 34 before it is applied again to the adder 30. This procedure is repeated over several fields or frames. Thus, an integrated value 20a of the shake information over the several fields or frames can be obtained.
The output 20a of the integration circuit 20 is used for compensating for the shake. Thus, it is a signal representing the amount of compensation and the direction of compensation, that is, a shake compensation signal. Based on this shake compensation signal 20a, the drive circuit 22 drives the variable angle prism 10 to a corresponding direction by a corresponding distance to those in and by which its amount of deflection of the image decreases to a minimum. It should be noted that there are limits on the total movement of the variable angle prism 10. As a violent camera shake occurs, or flowing shots are taken, or the shooting direction is changed, causing the so-called panning or tilting, when the limit is reached, therefore, a reset signal 10 is produced, which is supplied to the integration circuit 20 (more specifically, the memory 34). At the same time, the variable angle prism 10 also is returned to the initial angular position.
By such an operation as described above, even in a case where the camera shake has occurred in hand-held photography, the motion of the image can be automatically compensated for.
However, if, in the above-described conventional example, the photographer performs panning or tilting for a relatively long time, the variable angle prism 10 is caused to change in one direction with respect to the panning or tilting direction until it strikes on the limit of its allowable range of movement. As it is reset, the prism 10 moves back to the initial position. Then the compensating movement is started again. The repetition of such a procedure gives an alternative problem of making the picture uncomfortable to view.